Atrial Septal Defects (ASDs) are one of the most common types of congenital heart defects, and if left untreated can lead to severe cardiovascular complications. ASDs can often be successfully treated by percutaneous device closure, but the Nitinol-based ASD occlusion devices currently available in the U.S. are associated with infrequent, but significant long-term complications due to the stiff metal framework that remains in the heart for the remainder of the patient's life. We propose to develop a new shape memory ASD occlusion device with a poly(glycerol dodecanoate) (PGD) framework and small intestinal submucosal (SIS) extracellular matrix covering that is biocompatible and entirely biodegradable, can be delivered via a transcatheter delivery system, and can be deployed within an ASD with minimal residual shunting of blood. Bioresorbable devices will provide occlusion capabilities similar to current devices available, but offer the additional benefit of allowing the scaffolding to be resorbed once tissue overgrowth and complete closure has occurred. The PGD material will be characterized in terms of tensile mechanical properties and tearing strength, and prototype devices will be assembled. A pilot study will be performed in a large animal ASD model to assess short- and long-term occlusion of shunt flow, as well as endothelization, myocardial remodeling, and response to the implanted material. Ultimately, our goal is to create moldable PGD devices using patient-specific dimensions, improving the likelihood of successful device placement and increasing the number of patients eligible for percutaneous/transcatheter ASD closure. Successful completion of this project will form the basis for an NIH R01 application to develop and test a transcatheter delivery system for the PGD ASD occluders.